The present invention relates to claw cranes of the type having pushers, and more particularly the invention relates to such claw crane which is well suited for loading and unloading, transporting and stacking steel products such as blooms or the like.
The stacking of steel products (cast steel products) is frequently utilized for the purpose of transporting the products from one factory to another or temporarily storing the products within the factory. In this case, the stacking of such products has the following merits.
(1) The storage space area for steel products can be reduced, and moreover if freight cars, trailers or the like are used for transporting the products, their loaded weights can be increased with the resulting decrease in the number of the cars or trailers used. PA1 (2) Where the rolled steel products (or cast steel products) are hot charged into the subsequent processing units, the stacking of the steel products (or the cast steel products) has the effect of preventing drop in the temperature of the products.
In the past, it has been the usual practice to use a crane with a lifting magnet for stacking high-temperature steel products (or cast steel products), and the problem with the use of such crane is that according to the presently available techniques the attraction of such magnet is such that it is possible to lift only those products whose temperatures are lower than 600.degree. C. As a result, a method has recently been investigated in which the surface portion of steel product (or cast steel) tending to contact with the magnet is locally cooled to below 600.degree. C. so as to be lifted by the lifting magnet equipped crane, and this method has not come into use due to the anticipated danger of the steel product (or the cast steel) falling due to the regenerated heat, causing camber, bending or the like in the product due to the localized cooling and so on.
On the other hand, it is conceivable to use a crane of the tongs type for the stacking purposes. However, this method is also disadvantageous in that since the steel products (or the cast steel products) are lifted one at a time, the resulting crane cycle time is longer than the other cranes with the resulting decrease in transport efficiency, and moreover the spacing equal to the tongs width will be left between the stacked steel products thus inevitably decreasing the temperature of the products and also decreasing the loaded weight. Of course, it is conceivable to simultaneously lift a plurality of the products by the tongs. In this case, however, there is a great danger of the products falling and thus it is absolutely impossible to use this method.
Still another known stacking method uses a claw crane and this method is disadvantageous in that while there is no ill effect due to the product temperature, a distance member must be inserted between the steel products (or the cast steel products) to provide a claw withdrawing allowance with the resulting deterioration of the operation efficiency, and moreover the presence of spaces for distance member insertion allowance inevitably results in a considerable heat release and thus undesirable from the standpoints of slow cooling of the steel products and saving of energy.